The present invention relates to the field of mass storage devices. More particularly, this invention relates to an apparatus and method for motor speed control in a disc drive.
One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data is a computer system is on a disc drive. The most basic parts of the disc drive are a disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (xe2x80x9cABSxe2x80x9d) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting water that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc drive systems read and write information stored on tracks on storage discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. The transducer is also said to be moved to a target track. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track.
The data is divided or grouped together on the tracks. In some disc drives, the tracks are a multiplicity of concentric circular tracks. In other disc drives, a continuous spiral is one track on one side of a disc drive. Servo marks are written to the disc surface. The servo marks provide location information so that the radial position of the head with respect to the disc can be determined. The servo marks are wedges of servo information. Between the servo marks or fields, data is written. The servo marks are used to provide feedback information used to accurately locate the transducer. The write gate or the time when the disc drive writes data to the disc must be accurately controlled so that other information on the disc surface is not overwritten. The speed of the motor also must be accurately controlled to keep the spacing between the data bits consistent so that the spacing after writing is the desired or expected spacing between the bits. If the spacing is too close or too far apart, the disc drive will have difficulty in reading the data.
Generally, the velocity of the motor rotating the discs is checked by measuring the timing between servo marks on the surface of the disc. When the velocity drops or increases to a point outside the range of acceptable speed, the write operation is stopped. There is a problem with current systems. Servo firmware calculates velocity and declares an unsafe condition to prevent further writing. Typically, the unsafe condition is set some time after the motor speed is detected to be out of the range of acceptable speed or velocity limits. If this happens during a write operation, a number of data sectors will have already been written at an out of limit motor speed. When attempting to read the data sectors at a later time, the motor speed will be normal, and the data may be difficult or impossible to recover. One instance where out of limit motor speed occurs is during a power down failure in a disc drive. The motor slows due to the power down failure so that data is written to a sector or sectors at higher bit densities than expected. In other words, the bits are written closer together than normal. The end result is that the data is corrupted. It may be recoverable using deep data recovery techniques, such as changing the motor speed slightly. It also may be unreadable if the bits are too closely spaced and separate transitions can not be discerned.
What is needed is a disc drive that will either minimize the number of data sectors that are written when the motor is spinning at an out of limit speed or velocity, or a disc drive that will eliminate writing information when the motor is spinning at an out of limit speed or velocity.
An information handling system, such as a disc drive, includes a base, a disc stack rotatably attached to the base, and an actuator assembly movably attached to the base. Attached to one end of the actuator assembly is one or more transducers. The disc includes data areas and servo areas written at angular locations on the disc. The disc drive also has a disc drive controller which includes a motor speed controller, a write gate controller, and software for predicting the disc speed at an upcoming servo area and disabling the write gate if the predicted disc speed is outside a selected range of disc speeds. Predicating the disc speed may further include an abort signal generator that produces an inhibit write gate signal in response to the predicted disc speed being outside the selected range of disc speeds. Predicting the disc speed may also include a table of previous servo areas and disc speeds associated with the previous servo areas. Predicting the disc speed may also include software for fitting a trend line to a table disc speeds associated with a current servo area and at least one previous servo area.
The disc drive employs a method which includes calculating a predicted velocity at the next servo mark based on the measured velocities at a plurality of servo marks, comparing the predicted velocity to a range of reference values, and inhibiting the write operation when the predicted velocity is outside the range of reference values. Predicting the speed of the motor at the next angular location of the disc further includes plotting the speed of the motor at several previous angular locations of the motor, and determining a trend in the speed of the motor. Predicting the speed of the motor at the next angular location of the disc further may also include plotting the speed of the motor at several previous servo sectors which are determinative of the angular location of the motor, and determining a trend in the speed of the motor. Predicting the speed of the motor at the next angular location of the disc further may also include plotting the speed of the motor at several previous servo sectors on the surface of the disc to which data may be written. The servo sectors are determinative of the angular location of the motor. Plotting the speed of the servo sectors allows a trend in the speed of the motor to be determined. The write operation is aborted when the predicted speed is outside the selected range of speeds. The abort signal may be sent to a controller which controls the write operation. The write operation may also be aborted by sending an abort signal to a controller, and sending a write disable signal from the controller to the transducer.
A method for controlling the write operation in a disc drive is also disclosed. The method includes monitoring the speed of a motor, and predicting the speed of the motor at the next angular location of the disc. The predicted speed for the next angular location is compared to a selected range of speeds. The write operation is aborted when the predicted speed is outside the selected range of speeds. Predicting the speed of the motor at the next angular location of the disc includes plotting the speed of the motor at several previous angular locations of the motor, and determining a trend in the speed of the motor. The write operation is aborted when the predicted speed is outside the selected range of speeds. An abort signal is sent to a controller which controls the write operation. The write operation may also be aborted by sending an abort signal to a controller, and sending a write disable signal from the controller to the transducer.
Advantageously, predicting when the speed of the disc will travel outside of its limits, prevents or minimizes the number of sectors containing corrupted data. Another way of putting this is that the method will minimize or prevent writing data to a data area of the disc at an unacceptable data density. This invention also minimizes the number of unrecoverable errors or the number of write errors that need to use deep data recovery procedures. Deep data recovery procedures are used to read data when all else fails. The deep data recovery procedures take time. The performance of the disc drive is enhanced. Furthermore, the disc drive is more dependable over its life. In addition, the data stored on the disc drive using the apparatus and method is readable and less prone to error.